In recent years, following to the MPEG (Moving Picture Experts Group) which handles image data digitally, and, at that time, compresses the data by a discrete cosine transform or other orthogonal transform and motion compensation utilizing the redundancy peculiar to image information, as the purpose of transmitting and storing information with a high efficiency, a coding apparatuses and decoding apparatuses based on the H.264/AVC (Advanced Video Coding) and other coding schemes having higher compression ratios have been spreading in both distribution of information by broadcast stations etc. and reception of information at general homes.
Further, at present, work is underway for standardization of the SVC (Scalable Video Coding) extending the function of scalability based on this H.264/AVC. The current specifications of SVC are combined in the JSM (Joint Scalable Video Model).
In an SVC coding apparatus, an input image is divided by an image hierarchical (layering or layered data processing) circuit into two classes of for example an upper significant layer and lower significant layer. After that, an upper significant layer coding circuit encodes the upper significant layer, and the lower significant layer coding circuit encodes the lower significant layer. Then, the encoded upper significant layer and lower significant layer are multiplexed and transmitted.
The lower significant layer is also called as a “base layer” and is a layer having a low image quality. When decoding only a bit stream of the lower significant layer, an image having relatively low image quality is decoded. However, the lower significant layer includes more important information as the image quality.
The upper significant layer is also called as an “enhancement layer” and is a layer for enhancing the image quality and decoding an image having a high image quality.
When decoding a bit stream of the upper significant layer in addition to the bit stream of the lower significant layer, it is possible to decode an image having a higher image quality.
In the above coding apparatus, when the upper significant layer coding circuit performs intra-coding, a decoded image obtained by coding in the lower significant layer coding circuit, then decoding can be used as a predicted image.